THE STATE OF THE ART
Exploration for and production of oil and gas reserves underlying the oceans of the world are performed from offshore drilling facilities which usually are located some distance from the adjacent shore line. The drilling facility may be a tower erected on the sea floor and extending to a work platform above the water surface, or the drilling facility may be a floating platform. The floating platform may be either of the drillship type or of the semi-submersible type; in either event, the facility is located for long periods, perhaps even permanently, offshore often at substantial distances from the nearest available port or supply location.
An industry has developed to logistically support offshore drilling facilities. As presently defined, this industry is composed generally of independent contractors to the owners and operators of the offshore drilling facilities. These independent contractors own fleets of one or more supply vessels which, depending upon the areas in which they operate, are usually designed with reference to the particular climatic and sea conditions likely to be encountered. A typical offshore supply vessel is either designed specifically for a given limited purpose or as a compromise amongst the competing factors pertinent to other requirements of the logistics for offshore drilling facilities. An example of a special purpose vessel is a crew boat which is designed to ferry personnel to and from offshore drilling facilities. An example of a multifunction design compromise offshore support vessel is a work boat which, at various times in its life, is called upon to transport tubular goods such as drill pipes or production casing to the offshore drilling facility, or to transport food or dry or liquid bulk goods and supplies to the drilling facility, or to serve as an anchor-handling boat in connection with the initial positioning and mooring of a floating offshore drilling facility. Because a workboat typically constitutes a design compromise to enable the vessel to serve multiple functions, it is of less than optimum characteristics for the performance of any one function.
An offshore support vessel, such as a crew boat or a work boat, constitutes a substantial investment to its owner. Such vessels are idle much of their useful life since they must be tied up at the dockside at the shore-based supply location to take on and to discharge cargo; they are similarly idle for even longer periods in the course of discharging cargo to and receiving cargo from an offshore drilling facility. Transfer of cargo between an offshore drilling facility and a support vessel is generally a time consuming and hazardous process because the cargo must be transferred piecemeal by use of boom cranes and the like mounted on the drilling facility. These cargo transfer operations at the drilling facility often must be performed with respect to a support vessel which is pitching, heaving, and rolling as the vessel responds to passing wave trains. It is not uncommon for support vessels to be damaged or for cargo to be lost during this transfer process.
The specific patent references considered in the preparation of this patent application are as follows:
U.s. pat. Nos. 10,843Young, 1854; 1,076,068 Schleieher, 1913; 1,226,055, Bohn, 1917; 2,371,149, Bylo, 1945; 2,894,650, Black, 1959; 3,139,197, Bylo, 1964; 3,191,568, Schroeder, 1965; 3,349,742, Bylo, 1967; 3,399,792, Chester, 1968; 3,417,721, Vienna, 1968; 3,557,742, Gainsley, 1971; 3,793,974, Bylo, 1974; 3,934,532, Bylo, 1976; 1,022,374, Pedrick, 1966.